Direct current motor safety circuits for fluid delivery systems

ABSTRACT

A safety circuit system for a DC driven device for use with a fluid delivery system includes a first voltage potential DC power line, a second voltage potential DC power line, a controller and a safety circuit. The first voltage potential DC power line is coupled to provide a first voltage potential to the DC driven device, and the second voltage potential DC power line is coupled to provide a second voltage potential to the DC driven device such that the second voltage potential is different relative to the first potential. The controller controls at least the first voltage potential on the first voltage potential DC power line. The safety circuit has an enable state and a disable state, in which the default state is the disable state. The safety circuit is coupled to the controller, and the controller controls the safety circuit to place the safety circuit in the enable state independently of controlling the first voltage potential on the first voltage potential DC power line. The safety circuit is operatively coupled to at least one of the first and second voltage potential DC power lines to inhibit DC flow and operation of the DC driven device when the safety circuit is in the disable state and to permit DC flow and operation of the DC driven device when the safety circuit is in the enable state such that the operation of the DC driven device will occur when the safety circuit is in the enable state. In one version the DC driven device is a DC motor in an infusion pump, while in other versions the DC driven device is a gas generator in an infusion pump. Preferably, the safety circuit is controlled by an AC signal from the controller such that the safety circuit is enabled by the AC signal to permit DC flow and enable the forward motion of the DC motor while the AC signal is provided by the controller.

FIELD OF THE INVENTION

[0001] This invention relates to direct current (DC) motor safetycircuits in fluid delivery systems and, in particular embodiments, tosafety circuits for DC motors in medication/drug infusion pumps toinhibit accidental over delivery of medications/drugs due to DC motorcontrol circuit failures.

BACKGROUND OF THE INVENTION

[0002] Conventional drug delivery systems such as infusion pumps thatdeliver insulin over a period of time utilize a variety of motortechnologies to drive an infusion pump. Typical motor technologiesinclude direct current (DC) motors, stepper motors, or solenoid motors.Each motor type has various advantages and disadvantages related tocost, reliability, performance, weight, and safety.

[0003] In drug delivery using infusion pumps, the accuracy of medicationdelivery is critical (such as for insulin, HIV drugs or the like), sinceminor differences in medication quantity can dramatically affect thehealth of the patient. Thus, safeguards must be designed into thedelivery system to protect the patient from over or under delivery ofmedication. For example, in the case where insulin is administered viaan infusion pump to a diabetic patient, excessive drug delivery couldcause complications due to hypoglycemia, and could possibly even resultin death. Therefore, controlled delivery with safeguards against overdelivery of medications is required for drug delivery systems when overdelivery could result in complications, permanent damage, or death ofthe patient.

[0004] In conventional systems, these safeguards against over deliveryhave been incorporated into the drive systems of infusion pumps invarying ways. For example, the motor control electronics utilize crosschecks, encoder counts, motor current consumption, occlusion detection,or the like, as a form of feedback to guard against over or underdelivery of medication. However, one drawback to this approach can occurif the control electronics in a DC motor driven infusion pump were tofail, such that a direct short occurs from the power source to a DCmotor in the infusion pump. For example, in one failure mode, it wouldbe possible for the DC motor to drive continuously for an excessiveperiod of time, for example, until the power source was depleted orremoved, or until the short was removed. This condition is commonlyreferred to as motor “run away”, and could result in all of themedication contained in the infusion pump being infused immediately overtoo short a period of time resulting in injury or death to the patient.

[0005] To avoid this drawback, some infusion pump manufactures haveavoided the use of DC motors and have instead utilized solenoid orstepper motor technologies. With these motor types, any short in thecontrol electronics, would only result in, at most, a single motor step.Therefore, motor “run away” would not occur. Thus, this avoids theproblem of a “run away” failure. However, a drawback to the use ofsolenoid or stepper motor technologies is they generally have a lessefficient performance and tend to cost more as compared to the DCmotors.

SUMMARY OF THE DISCLOSURE

[0006] It is an object of an embodiment of the present invention toprovide improved DC motor safety circuits, which obviate for practicalpurposes, the above mentioned limitations.

[0007] According to an embodiment of the invention, a safety circuitsystem for a DC driven device for use with a fluid delivery systemincludes a first voltage potential DC power line, a second voltagepotential DC power line, a controller and a safety circuit. The firstvoltage potential DC power line is coupled to provide a first voltagepotential to the DC driven device, and the second voltage potential DCpower line is coupled to provide a second voltage potential to the DCdriven device such that the second voltage potential is differentrelative to the first potential. The controller controls at least thefirst voltage potential on the first voltage potential DC power line.The safety circuit has an enable state and a disable state, in which thedefault state is the disable state. The safety circuit is coupled to thecontroller, and the controller controls the safety circuit to place thesafety circuit in the enable state independently of controlling thefirst voltage potential on the first voltage potential DC power line.The safety circuit is operatively coupled to at least one of the firstand second voltage potential DC power lines to inhibit DC flow andoperation of the DC driven device when the safety circuit is in thedisable state and to permit DC flow and operation of the DC drivendevice when the safety circuit is in the enable state such that theoperation of the DC driven device will occur when the safety circuit isin the enable state. In preferred embodiments, the DC driven device is aDC motor in an infusion pump. Alternatively, the DC driven device is agas generator in an infusion pump. In preferred embodiments, the safetycircuit is controlled by an AC signal from the controller such that thesafety circuit is enabled by the AC signal to permit DC flow and enablethe forward motion of the DC motor while the AC signal is provided bythe controller.

[0008] In embodiments that utilize a DC motor, the safety circuit beingin the disable state operates to inhibit the forward motion of the DCmotor when the difference of the first voltage potential relative tosecond voltage potential is positive. In addition, the safety circuitbeing in the disable state is inoperative to inhibit a reverse motion ofthe DC motor when the difference of the first voltage potential relativeto second voltage potential is negative. Alternatively, or in additionto, the safety circuit being in the disable state operates to inhibit areverse motion of the DC motor when the difference of the first voltagepotential relative to second voltage potential is negative. In addition,the safety circuit being in the disable state operates to inhibit theforward motion of the DC motor when the difference of the first voltagepotential relative to second voltage potential is negative. Further, thesafety circuit being in the disable state is inoperative to inhibit areverse motion of the DC motor when the difference of the first voltagepotential relative to second voltage potential is positive.Alternatively, the safety circuit being in the disable state operates toinhibit a reverse motion of the DC motor when the difference of thefirst voltage potential relative to second voltage potential ispositive.

[0009] Preferred embodiments are directed to an infusion pump, in whichthe safety circuit is used to prevent operation of the DC motor during acontroller failure to prevent accidental delivery of excess fluid. Inparticular embodiments, the safety circuit is integral with the DCmotor. In other embodiments, the safety circuit is co-located with thecontroller.

[0010] Other features and advantages of the invention will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings which illustrate, by way of example,various features of embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A detailed description of embodiments of the invention will bemade with reference to the accompanying drawings, wherein like numeralsdesignate corresponding parts in the several figures.

[0012]FIG. 1 is a schematic diagram of a safety circuit in accordancewith a first embodiment of the present invention.

[0013]FIG. 2 is an illustrative schematic diagram of a safety circuit inaccordance with a second embodiment of the present invention.

[0014]FIG. 3 is a schematic diagram of a safety circuit in accordancewith a third embodiment of the present invention.

[0015]FIG. 4 is a schematic diagram of a safety circuit that is avariation of the embodiment shown in FIG. 3.

[0016]FIG. 5(a) is a schematic diagram of a safety circuit that is afurther variation of the embodiment shown in FIG. 3.

[0017]FIG. 5(b) is a top view of a pin out diagram for a component usedin the circuit shown in FIG. 5(a).

[0018]FIG. 5(c) is a top view of a pin out diagram for another componentused in the circuit shown in FIG. 5(a).

[0019]FIG. 6 is a schematic diagram of a safety circuit that is yetanother variation of the embodiment shown in FIG. 3.

[0020]FIG. 7 is a perspective view of a motor in accordance with anembodiment of the present invention.

[0021]FIG. 8 is a simplified schematic of a motor and safety circuit inaccordance with an alternative embodiment of the present invention.

[0022]FIG. 9 is a waveform diagram illustrating operation of the safetycircuit and power supplied to a DC motor in accordance with theembodiments of the present invention.

[0023]FIG. 10 is a waveform diagram illustrating operation of the safetycircuit and power supplied to a DC motor that is an enlarged view of theportion shown in the dashed circle 10-10 of FIG. 9.

[0024]FIG. 11 is a waveform diagram illustrating operation of the safetycircuit and power supplied to a DC motor that is an enlarged view of theportion shown in the dashed circle 11-11 of FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] As shown in the drawings for purposes of illustration, theinvention is embodied in safety circuits for direct current (DC) motorsused in fluid delivery systems. In preferred embodiments of the presentinvention, controllers that provide a signal to the safety circuit, inaddition to providing power for the DC motor in an infusion pump, thatenables the DC motor to operate only when an enabling signal is providedto the safety circuit. However, it will be recognized that furtherembodiments of the invention may be used to inhibit motor operation withadditional signals or by controlling other aspects of the infusion pump.The safety circuits are primarily adapted for use in infusion pumps thatdeliver medication (or fluid) to subcutaneous human tissue. However,still further embodiments may be used with infusion pumps for othertypes of tissue, such as muscle, lymph, organ tissue, veins, arteries orthe like, and used in animal tissue. The infusion pumps are alsoprimarily for external use; however, alternative embodiments may beimplanted in the body of a patient. The fluid delivery systems are alsoprimarily for delivery of medication, drugs and/or fluids to a patient;however other embodiments may be used with other fluid delivery systemsthat require a high degree of confidence that a DC motor “run away” willnot occur, such as in certain manufacturing techniques or the like.Preferred embodiments are directed to safety circuits for DC motors.However, alternative embodiments may be used with other DC drivendevices, such as a DC activated gas generator in an infusion pump or thelike.

[0026] Preferred embodiments are directed to circuits and methods forusing DC motor technology in fluid delivery systems with additionalsafety circuits to prevent DC motor “run away”. Use of this technologyobviates the need for the use of comparatively less efficient and moreexpensive stepper motor and solenoid motors. All of the illustratedembodiments include a DC motor and some DC motor control electronics,although other components or DC driven devices may be used. The controlelectronics may be relatively simple, such as only including thecapability of turning the DC motor on and off by supplying power for theduration of a key press, or may be more complex using microprocessorshaving multiple programmable control profiles utilizing feedback from anencoder, driving current or the like.

[0027]FIG. 1 illustrates a safety circuit 110 in accordance with a firstembodiment of the present invention. In this embodiment, a DC motor 112is configured to have a nominal voltage winding that is significantlyhigher then a supply voltage from a battery 114. To generate asufficient voltage to operate the DC motor 112, the safety circuit 110utilizes a DC-DC step up converter 116 (or similar), that includes anintegral controller 118, between the battery 114 and the DC motor 112 todrive the DC motor 112 at its rated voltage (see FIG. 1). Generally,when a DC motor is supplied with the rated voltage (and also assumingthere is sufficient current available), the DC motor will provide aknown torque. If, for example, the supply voltage is halved, then the DCmotor will only provide approximately half the full voltage outputtorque. However, a two, or more, times DC-DC step up converter could beutilized between the battery and the DC motor to provide the ratedvoltage to the DC motor. Thus, to provide a safety circuit, the nominalmotor voltage winding is selected to be some large multiple of thesupply voltage from the battery, such as ten times, or the like, higherthen the supply voltage from the battery. Therefore, if the battery 114is shorted directly to the DC motor 112 (i.e., as when there is ancontrol electronics 118 failure and/or DC-DC step up converter 116), theDC motor's 112 output torque would only be approximately {fraction(1/10)} of the rated value.

[0028] Generally, if the friction in the complete drive system (e.g.,drive gears, shaft, or the like) is approximately {fraction (1/10)} ofthe nominal rated value, the DC motor 112 will not have enough availabletorque to drive the system and cause a “run away” condition. To drivethe DC motor 112 with sufficient torque, a DC-DC step up converter 116would be required with approximately a ten times step up capability. Foradditional safety, alternative embodiments of the safety circuit 10would include the DC-DC step up converter 116 such that it would only beenabled by an additional internal signal S1 (shown in dashed lines) fromthe integral control electronics 118. Thus, if the control electronics118 were to fail, there would be no enable signal to provide therequired step up voltage to drive the DC motor 12 in a “run away”condition. Alternative embodiments may utilize different battery supplyvoltages to rated nominal motor voltages ratios, with the choice beingbased on system friction, tolerance for movement, cost of controlelectronics and DC motors, or the like. In further alternatives, thecontrol electronics 118 may be separated from the DC-DC step upconverter 116 and provided as a discrete element that is placed beforeor after the DC-DC step up converter 116.

[0029]FIG. 2 illustrates a safety circuit 200 in accordance with asecond embodiment of the present invention that builds upon theembodiment shown in FIG. 1. The safety circuit 200 utilizes a DC-DC stepup converter 202 (that includes integral control electronics 210) and aZener diode 204. The DC-DC step up converter 202 converts the supplyvoltage from the battery 206 to a value corresponding to the sum of therated motor winding voltage of the DC motor 208 and the Zener diode 204.For instance, if the DC motor 208 has 3.0 volt motor winding and theZener diode 204 has a breakdown voltage of 2.0 volts, the DC-DC step upconverter 202 must provide 5.0 volts to facilitate operation of the DCmotor 208 at its nominal rated voltage, if it is desired to drive the DCmotor 208 at the rated voltage. Thus, in this example, when the supplyvoltage from the battery 206 is stepped up to 5 volts as a positivevoltage potential, 2 volts are lost through the Zener diode 204 and 3volts are provided for operation of the DC motor 208. In the reversedirection (i.e. a negative voltage potential), the DC-DC step upconverter 202 only needs to step up the 1.5 volts supply voltage fromthe battery 206 to 3 volts, since there is little loss through the Zenerdiode 204 in the reverse direction. In an alternative embodiment, aSchottky diode 250 (shown in dashed lines in FIG. 2) may be placed inparallel with the Zener diode 204 to insure a low and predictablevoltage drop in the reverse direction (i.e., negative voltagepotential). Alternatively, if a higher speed rewind (e.g., more torque)is desired and/or required, the DC-DC step up converter 202 can still bestepped up to the 5 volts to over drive the 3 volt rated DC motor 208.Alternatively, the DC-DC step up converter 202 can provide a range ofvarious voltage values to drive the DC motor 208 at different ratings ineither the forward or the reverse directions.

[0030] In this embodiment, if the integral control electronics 210failed and caused a direct short between the battery 206 and the DCmotor 208 with the reversed biased Zener diode 202 (or a reversed biasedZener diode 202 in parallel with a Schottky diode 250), the DC motor 208would not operate in the forward direction (i.e., there would be no drugdelivery), and would have only a fraction of the rated torque in therewind direction (or no rewinding if sufficient friction is present inthe drive mechanism). For additional safety, alternative embodiments ofthe safety circuit 200 would include the DC-DC step up converter 202such that it would only be enabled by an additional internal signal S2(shown in dashed lines) from the control electronics 210. Thus, if thecontrol electronics 210 were to fail, there would be no enable signal toprovide the required step up voltage to drive the DC motor 208 in a “runaway” condition. In preferred embodiments, the Zener diode 204 iscontained within the DC motor package 212 (see also FIG. 7) so that theDC motor 208 is protected independently of the type of controlelectronics 210 to which the DC motor 208 is connected. In alternativeembodiments, the Zener diode 204 could be contained within the controlelectronics and the electronics are then connected to a conventional DCmotor (see also FIG. 8). In alternative embodiments, a second Zener maybe used, which is reversed with respect to the first diode and in serieswith the first diode such that the DC motor operates similarly in bothdirections. In the event of direct short to the DC motor in the reversedirection, the battery voltage would not be enough to run the motor 208in either direction. In further alternatives, the control electronics210 may be separated from the DC-DC step up converter 202 and providedas a discrete element that is placed before or after the DC-DC step upconverter 202.

[0031] In the first two embodiments, “run away” of the DC motor issubstantially prevented However, if the system were to fail such that ashort were maintained between the stepped up voltage from the DC-DCconverter to the DC motor and/or the Zener diode failed, then thepotential for motor “run away” exists with the above embodiments.

[0032]FIG. 3 illustrates a safety circuit 300 in accordance with a thirdembodiment of the present invention, which includes further enhancementsto provide protection against DC motor 302 “run away”. The safetycircuit 300 includes additional electronics added to the DC motorpackage (as shown in FIG. 7) that are independent of the controlelectronics. Alternatively, the additional electronics may be includedin the control electronics (as shown in FIG. 8) or as a separate set ofcontrol electronics (not shown). In preferred embodiments, the controlelectronics must provide a specific signal (at terminal 3) to theadditional electronics to allow the DC motor 302 to operate. As shown inFIG. 3, the rated supply voltage from the battery (not shown) issupplied to terminals 1 and 2 as a negative and positive voltagepotential, respectively, to control operation of the DC motor 302 in theforward direction. However, current will not pass through the DC motor302 until a specific AC signal (e.g., a 3 volt Peak-to-Peak Square waveat approximately 32 kHz—see FIGS. 9-11) is provided to terminal 3 andthe safety circuit 300 by the control electronics. This provides asecond independent system to control the operation of the DC motor 302.For a “run away” to occur the control electronics must short the batteryto the power terminals 1 and 3, and must also provide an AC signal toterminal 3 of the safety circuit 300. Thus, if a direct short does occurbetween the battery and the power terminals 1 and 3 with the safetycircuit 300, the DC motor 302 will not operate, since the required ACsignal at terminal 3 is not present. Preferably, the safety circuit 300uses two Schottky diodes 304 and 306 (e.g., BAT54SCT-ND from Zetex) anda FET 308 ((e.g., IRMLMS1902 from International Rectifier).

[0033] In operation, when the control electronics provide a positive DCvoltage potential at terminal 2, and a negative voltage potential atterminal 1, the DC motor 302 will not operate since the gate G of theFET 308 does not have a positive signal applied to it derived from theinput at terminal 3 of the safety circuit 300. In this situation, thegate G blocks the flow of current from the drain D to the source S ofthe FET 308. DC flow through terminal 3 is blocked by the capacitor C1.Thus, the DC motor 302 will not operate, if there is no AC signalapplied to terminal 3 of the safety circuit 300.

[0034] When an AC voltage potential signal (e.g., a 3 volt Peak to Peaksquare wave at a frequency of approximately 32 kHz—see FIGS. 9-11) isapplied to terminal 3 of the safety circuit 300, Schottky diodes 304 and306 rectify and double the signal to positively bias the gate G, currentthen flows from the drain D to the source S of the FET 308 and toterminal 1. This in turn drives the DC motor 302, which is connected tothe positive DC voltage potential at terminal 2. In alternativeembodiments, a different number of components, such as diodes,capacitors, resistors, or the like, may be used. In addition, theselection of the type of FET, diode, size of the voltage potentials onterminals 1, 2 and 3, the AC signal type (including duration of peaks,waveform and frequency), may be different, with the selection beingdependent on motor nominal operating voltage, system friction,tolerances, safety issues, control electronics, or the like.

[0035] In preferred embodiments, the safety circuit 300 uses theadditional AC signal to control the forward operation of the DC motor302, since concerns over DC motor “run away” arise mainly from thepossibility of over delivery of a fluid due to the failure of the safetycircuit 300. There is less concern for the situation, in which the fluiddelivery system rewinds, since no fluid would be delivered in thatscenario. However, in alternative embodiments, the drive system may alsouse an additional signal to control operation of the DC motor in therewind direction.

[0036]FIG. 4 illustrates a safety circuit 400 in accordance with afourth embodiment of the present invention. This safety circuit 400 issimilar to the embodiment of FIG. 3, but utilizes a BJT 402 (FMMT491ACT-ND from Zetex) instead of the FET 308, and an additional Schottkydiode 404 (e.g., BAT54CT-ND from Zetex).

[0037] FIGS. 5(a)-(c) illustrate a safety circuit 500 in accordance witha fifth embodiment of the present invention. This safety circuit 500 isalso similar to the embodiment of FIG. 3, but utilizes FET 502 (IRLM1902from International Rectifier) instead of the FET 308, and an additionalSchottky diode 504 (e.g., BAT54CT-ND from Zetex).

[0038]FIG. 6 illustrates a safety circuit 600 in accordance with a sixthembodiment of the present invention. This safety circuit 600 is similarto the embodiment of FIG. 3, but utilizes FET 606 (IRLM1902 fromInternational Rectifier) instead of the FET 308, and an additionalSchottky diode (e.g., BAT545CT-ND from Zetex). In addition, thecapacitors and resistors are selected to form a bandpass filter toprovide better noise isolation and circuit performance. Performance ofthe safety circuit 600 as it provides power to the DC motor 604 from abattery 602 is illustrated in FIGS. 9-11.

[0039]FIG. 7 illustrates a perspective view of a DC motor package 700that includes a safety circuit 702 within the package 700 holding a DCmotor 704. An advantage to this configuration arises from the fact thatthe DC motor 704 includes the safety circuit 702, which must beconnected, and enabled, or the DC motor 704 will not operate. Thisminimizes the possibility that a DC motor 704 will be improperlyinstalled in a fluid delivery device by assuring that an AC signal mustbe provided to the terminal input 3 on wire 706 to enable the DC motor704 to operate. In alternative embodiments, as shown in FIG. 8, thefluid delivery system 800 includes an additional safety circuit 802(i.e., in addition to other switches and controls found in the controlcircuitry), which is contained within the control electronics 804. Thecontrol electronics 804 are then connected to a standard, two-input DCmotor 806, without the need for an additional connection to the DC motor806. For instance, the safety circuit 802 operates a switch 808 toenable power to pass to and drive the DC motor 806.

[0040] FIGS. 9-11 illustrate operational waveforms for the safetycircuit 600 (see FIG. 6) as DC current is applied to the circuit. Asshown in FIG. 9, when DC current is applied to the DC motor 604 in graphsection 902, no current is drawn since the AC enable signal in graphsection 908 is not present. When the AC signal is applied in graphsection 910, the DC current is quickly applied to the DC motor 604 bythe battery 602, as shown by the graph section 904. When the AC enablesignal is removed, as shown in graph section 912, the DC power suppliedto the DC motor 604 is cutoff, as shown in graph section 906. FIGS. 10and 11 highlight and expand portions of FIG. 9 to illustrate the ACsignal used and the response of the safety circuit 600. The illustratedAC signal is at approximately 3 volts peak-to-peak at a frequency ofapproximately 32 kHz. However, in alternative embodiments, differentshape waveforms, such as saw tooth, sinusoidal, or the like may be used.In addition, different voltage ranges may be used, with the selectionbeing dependent on the rated motor output and the application in whichthe motor is being used. Further, higher or lower frequencies may beutilized, with the selection be dependent on the responsecharacteristics of the safety circuit, noise, or the like. The delaysobserved in FIGS. 10 and 11 are a result of the smoothing and bandpassfilters used in the safety circuit 600. For instance it takesapproximately 125 microseconds for the DC motor 604 to respond after theAC signal is provided, and about 80 microseconds for the DC motor 604 torespond to termination of the AC signal. One advantage of having the DCcurrent ramp up and down is that it minimizes the effects of voltagespikes and electromagnetic interference.

[0041] While the description above refers to particular embodiments ofthe present invention, it will be understood that many modifications maybe made without departing from the spirit thereof. The accompanyingclaims are intended to cover such modifications as would fall within thetrue scope and spirit of the present invention.

[0042] The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims, ratherthan the foregoing description, and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced therein.

What is claimed is:
 1. A safety circuit system for a DC motor for usewith a fluid delivery system, the safety circuit system comprising: afirst voltage potential DC power line coupled to provide a first voltagepotential to the DC motor; a second voltage potential DC power linecoupled to provide a second voltage potential to the DC motor, whereinthe second voltage potential is different relative to the firstpotential; a controller that controls at least the first voltagepotential on the first voltage potential DC power line; a safety circuithaving an enable state and a disable state, wherein a default state isthe disable state, wherein the safety circuit is coupled to thecontroller, wherein the controller controls the safety circuit to placethe safety circuit in the enable state independently of controlling thefirst voltage potential on the first voltage potential DC power line,and wherein the safety circuit is operatively coupled to at least one ofthe first and second voltage potential DC power lines to inhibit DC flowand forward motion of the DC motor when the safety circuit is in thedisable state and to permit DC flow and forward motion of the DC motorwhen the safety circuit is in the enable state such that the forwardmotion of the DC motor will occur when the safety circuit is in theenable state.
 2. The safety circuit system according to claim 1, whereinthe safety circuit is controlled by an AC signal from the controllersuch that the safety circuit is enabled by an AC signal to permit DC toflow and enable the forward motion of the DC motor while the AC signalis provided by the controller.
 3. The safety circuit system according toclaim 1, wherein the safety circuit in the disable state operates toinhibit the forward motion of the DC motor when the difference of thefirst voltage potential relative to second voltage potential ispositive.
 4. The safety circuit system according to claim 3, wherein thesafety circuit in the disable state is inoperative to inhibit a reversemotion of the DC motor when the difference of the first voltagepotential relative to second voltage potential is negative.
 5. Thesafety circuit system according to claim 3, wherein the safety circuitin the disable state operates to inhibit a reverse motion of the DCmotor when the difference of the first voltage potential relative tosecond voltage potential is negative.
 6. The safety circuit systemaccording to claim 1, wherein the safety circuit in the disable stateoperates to inhibit the forward motion of the DC motor when thedifference of the first voltage potential relative to second voltagepotential is negative.
 7. The safety circuit system according to claim3, wherein the safety circuit in the disable state is inoperative toinhibit a reverse motion of the DC motor when the difference of thefirst voltage potential relative to second voltage potential ispositive.
 8. The safety circuit system according to claim 3, wherein thesafety circuit in the disable state operates to inhibit a reverse motionof the DC motor when the difference of the first voltage potentialrelative to second voltage potential is positive.
 9. The safety circuitsystem according to claim 1, wherein the fluid delivery device is aninfusion pump, and wherein the safety circuit is used to preventoperation of the DC motor during a controller failure to preventaccidental delivery of excess fluid.
 10. The safety circuit systemaccording to claim 1, wherein the safety circuit is integral with the DCmotor.
 11. The safety circuit system according to claim 1, wherein thesafety circuit is co-located with the controller.
 12. A safety circuitsystem for a DC driven device for use with a fluid delivery system, thesafety circuit system comprising: a first voltage potential DC powerline coupled to provide a first voltage potential to the DC drivendevice; a second voltage potential DC power line coupled to provide asecond voltage potential to the DC driven device, wherein the secondvoltage potential is different relative to the first potential; acontroller that controls at least the first voltage potential on thefirst voltage potential DC power line; a safety circuit having an enablestate and a disable state, wherein a default state is the disable state,wherein the safety circuit is coupled to the controller, wherein thecontroller controls the safety circuit to place the safety circuit inthe enable state independently of controlling the first voltagepotential on the first voltage potential DC power line, and wherein thesafety circuit is operatively coupled to at least one of the first andsecond voltage potential DC power lines to inhibit DC flow and operationof the DC driven device when the safety circuit is in the disable stateand to permit DC flow and operation of the DC driven device when thesafety circuit is in the enable state such that the operation of the DCdriven device will occur when the safety circuit is in the enable state.13. The safety circuit system according to claim 12, wherein the DCdriven device is a DC motor, and wherein the fluid delivery system is aninfusion pump.
 14. The safety circuit system according to claim 12,wherein the DC driven device is a gas generator, and wherein the fluiddelivery system is an infusion pump.
 15. The safety circuit systemaccording to claim 15, wherein the safety circuit is controlled by an ACsignal from the controller such that the safety circuit is enabled by anAC signal to permit DC flow and enable the forward motion of the DCmotor while the AC signal is provided by the controller.